This invention relates to a rotary forging or upsetting machine.
Rotary forging or upsetting machines which utilize the plastic deformation of metal are known. In some known machines the workpiece is stationary in terms of rotation about the machine vertical axis and the lower platen with the workpiece is moved in the direction of the applied force relative to the vertical axis of the machine and the upper platen. In other known machines the workpieces are stationary with provision made to move the upper platen assembly in the direction of the machine vertical axis and provision for applying the desired force. This is achieved by the use of a combination of a hydraulically operated cylinder together with hydrostatic bearings to provide rotary drive and `wobbling`. All are incorporated in the upper platen assembly and the lower platen is maintained stationary.
The known designs lead to complex kinematic arrangements which are inherently costly and liable to failure.
The principle of rotary forging is shown in FIG. 1 and the relationship between angular velocities of the upper and lower platen and a point in the plastically deforming region will now be described generally. A conical upper platen 10 has a semi-angle (.pi./2)-.alpha. about an axis Z.sub.2 which is at an angle .alpha. to the vertical axis Z.sub.1. The axes Z.sub.1 and Z.sub.2 intersect at the point 0. Plastic deformation of the workpiece 11 is caused by the application of force F to the lower platen 12 in the direction of axis Z.sub.1.
Consider a point Q in a plastically deforming region which is at radius r.sub.1 and rotating about the axis Z.sub.1 of the workpiece 11 in the plane OR at an angular velocity .omega..sub.1. The instantaneous velocity of the point P in the plastically deforming region, tangential to the circle of radius r.sub.1 is given by EQU V.sub.1 =.omega..sub.1 r.sub.1
Let the point P in the plastically deforming region be coincident with a point Q on the surface of the conical platen 10 at a distance r.sub.2 from the axis Z.sub.2. Let point Q be moving at an instantaneous velocity V.sub.2 tangential to the circle radius r.sub.2, then EQU V.sub.2 =.omega..sub.2 r.sub.2
where .omega..sub.2 =angular velocity about Z.sub.2.
If at point P no slip takes place between the surface of the workpiece 11 in the plane OR and the surface of the conical platen 10, EQU then V.sub.1 =V.sub.2 EQU or .omega..sub.1 r.sub.1 =.omega..sub.2 r.sub.2 EQU but r.sub.2 =r.sub.1 cos .alpha. EQU therefore .omega..sub.1 r.sub.1 =.omega..sub.2 r.sub.1 cos .alpha. EQU (.omega..sub.1 /.omega..sub.2)=cos .alpha.
Thus, the plastically deforming region may be caused to rotate about the axis of the workpiece with no slip occurring in the plane OR by any combination of angular velocities which satisfy the equation (.omega..sub.1 /.omega..sub.2)=cos .alpha..
A known configuration which satisfies the equation is for the lower platen 12 together with the workpiece 11 to be maintained stationary relative to the axis Z.sub.1 and the axis Z.sub.2 rotated at an angular velocity .omega..sub.1 about the axis Z.sub.1 whilst the upper conical platen 10 rotates at an angular velocity .omega..sub.2 about the axis Z.sub.2.
This relative motion is known as "wobbling" and has been used in rotary forging machines to date.
Another known configuration which satisfies the equation is for the upper platen to be maintained stationary relative to the axis Z.sub.2 and the axis Z.sub.1 rotates about the axis Z.sub.2 at an angular velocity .omega..sub.2 whilst the lower platen together with the workpiece 11 rotates at an angular velocity .omega..sub.1 about the axis Z.sub.1.
Thus, the workpiece 11 and lower platen 12 is "wobbling" about the fixed upper conical platen.
In each of the arrangements described above it is necessary to provide for force and displacement between the upper conical platen 10 and the workpiece 11 in the direction of axis Z.sub.1. This is achieved by maintaining either the upper platen 10 or lower platen 12 stationary in terms of axial displacement relative to axis Z.sub.1 and displacing the other member accordingly. The desired relative axial displacement can also be achieved by displacing both the upper platen 10 and the lower platen 12 simultaneously. The force F can be applied by a screw-jack or hydraulic jack.
The most favoured arrangement is the second configuration referred to above with the additional facility to vary the angle .alpha..
British Patent Specification No. 1,224,260 shows a machine where angle .alpha. can be adjusted but adjustment can only be made when the machine is stationary. It is therefore not possible to adjust .alpha. continuously during the forging process.
U.S. Pat. No. 3,523,442 permits .alpha. to be adjusted continuously during the forging process but requires a third, almost concentric, bearing.
In the known configuration described above two separate degrees of freedom are required which are almost concentric about either the Z.sub.1 or Z.sub.2 axes since, for practical considerations .alpha..ltoreq.15.degree.. If a facility is provided to vary .alpha. during the process it may be necessary to introduce a third degree of freedom about the Z.sub.1 or Z.sub.2 axes.
The known arrangements require constraint of forces due to gyroscopic couples. These arise from the axes of rotating masses being displaced in space. It can be seen that due to plastic deformation of the workpiece in the direction OR, forces will exist between the upper platen 10 and the workpiece 11 in that direction. The radial displacement of the axis of the upper platen 10 relative to the axis of the lower platen 12 and workpiece 11, will depend upon the radial force and the sum of the radial compliance of the individual bearing systems. Manufacturing applications can arise where the tools designed to achieve a desired shape or form cause radial deformation of the workpiece. Relative radial displacement of the axes will cause errors in geometry of the workpiece and poor quality of surface finish due to angular velocity relationships which do not comply with the requirements to satisfy the equation (.omega..sub.1 /.omega..sub.2)=cos .alpha..
Any sliding which occurs between the upper platen 10 and workpiece 11 will lead to tool wear and the possibility of reduction in surface finish quality of the workpiece. In the known designs of machine the radial compliance of the individual bearing system is accumulative and leads to the upper platen sliding radially relative to the workpiece.